Available Options after legal notice for agreement to sell

Hello, thank you for having such a forum of helping someone like us. 1. I am the vendor signed an agreement to sell my 1000 square meters of land out of 10000 square meters of land that I own to a Purchaser 60 days ago. 2. One of a pre-condition purchaser put in the agreement was for me to get E-Khata at the time of registration to to check if I am the genuine owner. 3. I got the E-Khata within 30 days from signing the agreement and notified them to go for registration at their convenient time within agreed 60 days agreement time. 4. 40 days from signing he agreement the Purchaser came back and said he wanted E-Khata for only 1000 square meters of the land and not the E-Khata for the entire portion of the land. This was not clearly written in the written agreement. 5. 40 days from the signing the agreement the Purchaser emailed me on that he wants to cancel the agreement since I did not produce the E-Khata. 6. He also sent a legal notice asking me to pay 500000 as liquidated damages since I did not produce the E-khata for 1000 square meter alone. 7. Both agreement validity and legal notice period ends on 6-March-2016. 8. On 1st-March-2016, (6 days prior to ending both agreement and legal notice validity) I sent him an E-Khata for 1000 square meters alone and asked him to go for registration. 9. On 4-March-2016 (2 days prior of end validity of Agreement), I also replied to his legal notice by a registered post notifying the purchaser that the E-Khata is available and its already sent to him and asked him to register the property. 10. Purchaser is not responding to any form of communication Since the purchaser is engaging a known litigant lawyer, can you please advise the best option available for the Vendor?